Peter Siddle's new health regime will be put to the ultimate test if he backs up for the third test in Perth.

Siddle hasn't converted any teammates to the life of a teetotaling vegetarian, but the fast bowler's warrior-like performance on day five of the second test on Monday has earned him great respect from the dressing room and opposition alike.

"For him to recover, I don't know what he's going to have to do," said Steyn.

"Our physio reckons every time he runs a half marathon, and runs another half marathon a couple of days later, he can still feel the effects of the previous one.

"So I think if you can compare it, it's pretty similar to what Siddle has put himself through."

Siddle said he's never felt worse on a cricket field than he did on Monday trying to valiantly stop South Africa getting a draw out of the second test.

He described the feeling as "delirious".

However, the 28-year-old believes his new-found lifestyle has given him the confidence to believe his body will bounce back.

"I've actually recovered a lot better than I thought I would," Siddle said.

"It was obviously sore that night, but the last two days I've been waking up and feeling better and better, and I'm recovering a lot quicker.

"Everything's moving a lot better and I'm feeling a lot healthier.

"Being vegetarian is playing a big part and no alcohol has topped that off nicely. It's all working well at the moment and hopefully I can keep performing well and keep the body fit and strong."

Siddle said it was satisfying to see such obvious benefits come from his dedication to getting the best out of his body and his time at the top.

"All that training that you go through pre-season, all that work with your diet and your health and everything, it all comes down to days like that when you get to test yourself out and see how you're going to stand up," he said.

"The last couple of nights, I sat back and thought of all the sacrifices I've made for the body and all the work I've done to get me to that stage where I knew I could keep pushing through and pushing for the team and the captain in those last few overs."